Airplane fabric and method of manufacturing air frames



Patented Aug. 8, 1950 'No Drawing. Continuation"ofapplicationxSeriM No. 436,412,-March 27, 1942.5 This applicatio December 5,1946, Serial No."3214,1281

This invention relates tojanimprovied coated airplane fabric and more particularly to a sysg te'm or process of preparing'airplane partsusing such coated airplane fabric-which greatly shortens this time-consuming step'in the manufacture of aircraft.

, 2 further object is'the reduction in theQnumber" of coatings and other operations required in finishing fabric surfaces which are essential This application is a continuation of copenda ing application Serial No. 436,412, filed March 2'7, 1942, now abandoned.

In the construction of modern aircraft, both for civil and for military purposes, even for ships which are substantially all metal, numerous parts, for example, control surfaces such as rudders, elevators, flaps and ailerons, are providedfwith a fabric surface. In the specification and claim such parts are called air frames for simplicity. In practice an uncoated fabric is tightly stretched over the air frame by tailoring onto the frame a fabric sock which is deliberately prepared under-size in order to make it more tightly fitting. A clear cellulose derivative dope, usually. two brush coats, is then applied to the fabric surface to lay the nap of the. fabric and to function as'a size coat for subsequently ap-" plied top coats. Two to four clear cellulose derivative coatings are then sprayed over the base coat followed by two to four cellulose derivative me ings containing coloring matterjfE'ach coat is dried and sometimes sanded before the application of the following coat. This "system which requires a considerable number of operations, presents many application problems and, in addition, is undesirably time-consuming particularly in the present-day production line construction of military aircraft where a single bot-l tle neck serves to greatly retard maximum production. I 1

It has been proposed to predopethe. fabric prior to tailoring it onto the air frame and tests have been carried. out in which the fabric has been precoated with conventional dope coating compositions. However, this method provides a coated fabric which is quite boardy and which .is diflicult to handle and tailortothe airframe, thereby counteracting any advantage that might accrue through the precoating of the fabric. prior toits use in the aircraft factoryf I The process of the present invention,'however, overcomes these disadvantages and provides a method for greatly speedingup the production of military aircraft. j

This invention, therefore, has as a primary'ob in'the manufacture of military and civil aircraft. i'Anoth'er object is the provisionof a method for coating airplane fabric which provides satisfactoryitauteningof the fabric after it is attached't'oj the'air frames.

'A fother object is the provision of a composi tioniwhich affords a smoother finish by more effectively laying the nap and which also avoids x the necessity for sanding.

Anothero'bject is the provision of a system for finishing airplane fabric which provides greater suppleness'and pliability of the fabric, thereby greatly assisting in tailoring the fabric to the air frames.

A still further object is the provision of a com-' positionwhich provides a discontinuous film adjacent to the fabric which subsequently is ren dered continuous by the application of top coat dope coatings containing solvents for the discontinuous film. I

A"-still further object of the invention is the provisionof apliable predoped airplane fabric whichwgreatly facilitates the tailoring of the fabric to, theair framesand which affords better working properties.

ject the provision of a method for covering air doping schedules.- 1

,.These objects are accomplishedby the application of a cellulose derivative emulsion preferably free of resin and wax to the vsurface of an airplane fabric, said emulsion being so formulated as-to be totally deposited as a precipitated film which is discontinuous in nature. r

The. following examples are given by way of illustration onlyand no limitations are intended thereby except as indicated in the appended claims.

Example 1.-Cellulose nitrate emulsion (spray coating) Per cent by weight The viscosity characteristic of the nitrocellulose is 5 seconds determined in accorac'nce With A. S. T. M. Specification D-30l-33,

Formula A,

ous dispersion is secured. The second portion was then charged into a kneading machine and the first portion added gradually during continued kneading. This kneading action was continued until emulsification was complete; i. c., when the first portion was dispersed as globules within the second portion which forms the continuous phase. By complete emulsification is meant when a uniform predetermined particle size is reached which may be determined by mi- 'croscopic examination. In the present instance the particle size was approximately 12 microns.

The emulsion composition was thinned with water in the ratio of 3 parts of emulsion to 1 part of water and two coats of the thinned material applied by spraying onto airplane fabric consisting of Grade A Flightex mercerized cotton sheeting. having a thread count of between 80 and 84 in both the warp and filler direction and weighing approximately 4.0 oz. per square yard. The first coat was dried at room temperature for about 45 minutes before application of the second coating. The resulting finish was a whiteappearing, discontinuous coating which leaves the ;cloth very pliable and supple and readily adapted to tailoring onto an air frame. .The Weight of the coating when dried was approximately 1 oz. per square yard.

The fabric coated as described above was stretched over a frame and one double coat of the following conventional pigmented dope thinned as described was applied by spraying.

Percent by weight The viscosity characteristic of the nitroceluloge I i s seconds determined in accordance with A. Specification D-30l-33, Formula A.

Before spraying this composition onto the precoated fabric, it was thinned with equal parts of the following thinner:

. Percent by weight Butyl acetate 20.5

Methyl ethyl ketone 8.6 Ethyl alcohol (denatured) 9.5 Butyl alcohol 9.0 High solvency petroleum naphtha (135- 190 C.) 2.3 High solvency petroleum naphtha C.) -4 27.6 Petroleum naphtha (88 131 C,) 22.5

This treatment caused the base coat to become a continuous film by action of the solvents present in the top coat which dissolved and coalesced the discrete particles comprising the base coat. Considerable shrinkage occurred upon evaporation of the volatile solvents, thus affording the desired tautening effects.

A tautness determination by McGowan Tautness Meter showed a deflection of .091 inch which represents a satisfactory tautness.

The McGowan 'I'autness Meter is described in "Physical and Chemical Examination of Paints, varnishes, Lacquers and Colors, page 430 by H. A. Gardner, 9th ed., 1939.

The precoated fabric of the present invention when coated with one or more conventional dope compositions such as illustrated above will proyide a tautness such that a deflection of less than .110 inch is obtained on the McGowan Meter, which is satisfactory for the purpose described.

Example 2.-Cellulose nitrate emulsion (for knife The viscosity characteristic of the cellulose nitrate is 5 seconds determined in accordance with A. S. T. M. Specification D301-33, Formula A.

This composition was prepared by the procedure shown for the preparation of the emulsion of Example 1.

100 parts by weight of the above composition were thinned with 12 parts by weight of water and the thinned material then continuously knife-coated by conventional methods onto a water-dampened airplane fabric traveling at the rate of 7.5 yards per minute. The coating was dried by passing the coated fabricthrough a drying tunnel at the temperature of F. Two coats were applied in this manner. The resulting coating which was discontinuous gave a prodnot which was soft and pliable and easily tailored onto an air frame. The coated fabric was stretched tightly over a frame and one spray coat of the conventional pigmented dope shown in Example 1 applied by spraying. This treatment gave a final finish which was uniformly smooth and caused a satisfactory tautening of the fabric on the frame.

In addition to the cellulose nitrate shown in the examples, other water insoluble film forming cellulose derivatives such as ethyl cellulose, cellulose acetate and the mixed esters, for example, cellulose acetobutyrate and cellulose acetopropionate may likewise be employed with proper plasticizers and suitable volatile solvents so proportioned with regard to the water in the emulsion composition as to provide a discontinuous finish upon evaporationof the volatile constituents. Cellulose acetate and ethyl cellulose are not preferred for airplane fabric coatings because of their tendency to lose tautness but they are operable in the process and may be useful for coat- =ing other of fabrics. In any event, it is desirable discontinuity in--the' undercoat.- The solids composition of the coating are preferably similar to conventionalx'dope' compositions, The plasticizer; ratio/should hev relatively low, preferably in the proportion of 10 parts of nitrocellulose to l to 4 p'arts"of-plasticizer. Any substanfi e iiahi r' t ri otpl i i e r s 1 desirable reduction in tauteningeffects when the top coats are applied anddried,

The emulsion composition"as"employed in the improved system of the present invention'ffor finishing fabric parts o-f-aircraftshould besub- "stanti'ally free ofresin and waxsince materials of this type tendto cause embrittleme'nt-o'f the fin'ish,- atendency whichcannot be tolerated for the present purpose where a highfdegreeflexibility and pliability are "'of paramount-importance.

It is also necessary to include in the emulsion composition sufficient of non-solvent for the cellulose derivative, preferably water, to cause'precipitation of the nitrocellulose whereby a film of discontinuous nature is secured. To accomplish this, the non-solvent portion of the volatile vehicle should be present in an amount at least equal to the active solvent portion. Preferably the nonsolvent content will be about 1 to 3 times that of the solvent portion depending largely upon the solvent power and evaporation rate of the solvent portion of the vehicle.

The active cellulose derivative solvents employed in the compositions of the invention should not be completely miscible or soluble in water and in general it is preferred that they be not more than about 30% miscible with water. Furthermore, the evaporation rate of these solvents should be at least equal to and preferably greater than that of water or other non-solvent comprising that part of the vehicle in order that the cellulose derivative. may be substantially completely precipitated during evaporation of the volatile vehicle and not become the more residual part of the volatile vehicle to cause coalescence of the cellulose derivative, thereby forming a continuous film. If the volatile vehicle is prepared in accordance with the above limitations, the resulting film when applied to a fabric base will be discontinuous as hereinafter defined. For compositions in which the cellulose derivative is cellulose nitrate, ethyl acetate, methyl ethyl ketone, butyl acetate and methyl isobutyl ketone are satisfactory.

The compositions adapted for the purposes of the present invention may, as illustrated in the examples, contain aliphatic and aromatic hydrocarbon diluents such as toluene, benzol and petroleum naphthas such as gasoline fractions. Alcohols, preferably those which are not completely miscible with water, may also be included in the volatile vehicle.

In some instances where a higher degree of water-resistance is desired, it is possible to include in the emulsion composition which may contain water soluble emulsifying agents, such as polyvinyl alcohol, a small proportion of an insolubilizing agent such as stearato chromic chloride described in U. S. Patent 2,273,040 to Ralph K. Iler or dimethylol uron dimethyl ether as described in co-pending application S. N. 438,- 949, now Patent No. 2,373,135 to Maxwell. In preparing the emulsion, such as Example 1. which 6 may be modified-by the inclusion of the uron derivative, it has been found necessary in order to obtain'satisfactory stability of the emulsion toincorporate the insolubilizing agent in the first portion and the aluminum chlorideor other cat- 'alyst'in' the second portion of the emulsion.

'It is-al'so possible, and in some cases prefer able, to-apply the emulsion coating directly 'toa previously wetted fabric since this expedient may facilitate'deposition' by precipitation ofthe discontinuous type film. I

" -While "in some'cases 'satisfactoryresults can beobtairred by the use of a single top coat,'it is usually preferable to apply two or more dope coa-t's to-affOr bette r durability'andto increase tautnessi I l Although not required'for the successful operation of the invention, the fabric carrying the precipitated coating may be passed through heated --p'olished rolls under pressure tosmooth out the coating thereby contributing to the smoothness of the final finish.

' The primary advantage of the invention is the marked saving in time and labor required at the airplane factory for finishing parts which involve the use of fabric covering. This is particularly important in the manufacture of military aircraft where all bottle necks tending to retard production must be obviated. The new process permits desirable reduction in the number of operations in the preparation of the coated fabric. The practice of the present invention permits the elimination of at least one dope coat in the finishing schedule and in some instances satisfactory results are obtained with the elimination of as many as 3 to 4 dope coats from the schedule. The new system affords satisfactory tautness in the finished fabric and durability in service is also at least equal in all respects to that secured by older methods. The new method of predoping the fabric more completely lays the nap, thus avoiding necessity of sanding operations, and provides a finish which is smoother than that obtained by other predoping methods. The fabric coated in accordance with the present invention carries a discontinuous film which afl'ords superior pliability and suppleness, thereby facilitating tailoring of the fabric to the air frames. This also contributes greatly to the speeding up of operations and ultimate increase in aircraft production.

In the description and appended claims, a discontinuous coating is meant to define a coating which results from the precipitation of the cellulose derivative by the presence of an excess amount of non-solvent for the cellulose .derivative during evaporation of the solvent vehicle, the resulting film after drying consisting substantially of noncoalesced, discrete particles or disconnected aggregates of small particles.

It is apparent that many widely different embodiments of this invention may be made without departing from the spirit and scope thereof; and, therefore, it is not intended to be limited except as indicated in the appended claims.

We claim:

1. The process of manufacturing airplane air frames which comprises coating a strong lightweight woven fabric with an aqueous emulsion of a cellulose derivative, the oil phase of which contains the cellulose derivative and a solvent, the evaporation rate of the solvent being greater than that of the water allowing the volatile Vehicle to evaporate leaving a, discontinuous coat- '7 ing of discrete particle on the fabric, the said vehicle containing from about 1 to 4 parts of a solvent plasticizer for each 10 parts of the cellulose derivative, tailoring the coated fabric into alsock, fitting the same tightly over the air frame, and subsequently shrinking the said fabric to a tautiness deflection of less than about .110 inches by treating the said cellulose derivative with a solvent therefor.

'2. The process of claim 1 in which the cellulose derivative is cellulose nitrate.

3. The process of claim 1 in which the water is present in amount at least equal to the amount of solvent.

4. The process of claim 1 in which the nonsolvent is present in amount equal to about 1 to 3 times that of the solvent.

.5. A predopecl airplane fabric characterized by a high degree of suppleness and pliability having a precipitated coating thereon of a composition having the following formula:

DRE'YLING. CHARLES JOHNSON. REFERENCES crrnn The following references are of record in the file of this patent:

UNITED STATES .PA'IIV'ENTS Number Name Date 1,357,541 Cahill Nov. 2, 1920 1,391,890 Gault Oct. 25,1921 1,552,808 Sulzer Sept. 8, 1925 1,940,212 Given'et a1. Dec. 19, 1933 2,336,266 Lester Dec. 7, 1943 1,356,927 Grossman- Aug. 29, 1944 

1. THE PROCESS OF MANUFACTURING AIRPLANE AIR FRAMES WHICH COMPRISES COATING A STRONG LIGHTWEIGHT WOVEN FABRIC WITH AN AQUEOUS EMULSION OF A CELLULOSE DERIVATIVE, THE OIL PHASE OF WHICH CONTAINS THE CELLULOSE DERIVATIVE AND A SOLVENT, THE EVAPORATION RATE OF THE SOLVENT BEING GREATER THAN THAT OF THE WATER ALLOWING THE VOLATILE VEHICLE TO EVAPORATE LEAVING A DISCONTINUOUS COATING OF DISCRETE PARTICLES ON THE FABRIC, THE SAID VEHICLE CONTAINING FROM ABOUT 1 TO 4 PARTS OF A SOLVENT PLASTICIZER FOR EACH 10 PARTS OF THE CELLULOSE DERIVATIVE, TAILORING THE COATED FABRIC INTO A SOCK, FITTING THE SAME TIGHTLY OVER THE AIR FRAME, AND SUBSEQUENTLY SHRINKING THE SAID FABRIC TO A TAUTNESS DEFLECTION OF LESS THAN ABOUT .110 INCHES BY TREATING THE SAID CELLULOSE DERIVATIVE WITH A SOLVENT THEREFOR.
 5. A PREDOPED AIRPLANE FABRIC CHARACTERIZED BY A HIGH DEGREE OF SUPPLENESS AND PLIABILITY HAVING A PRECIPITATED COATING THEREON OF A COMPOSITION HAVING THE FOLLOWING FORMULA: 